In many stored energy combustors, air consumption grossly exceeds desirable levels which can often be attributed to high combustion inefficiency. This is typically due to heat loss from the flame to cold combustor walls, and it is further exacerbated by very low blow down air temperature entering the flame as flow which may reach, e.g., -190.degree. F. Still further, the problem is complicated by the high heat loss to the combustor wall because of the typically short transient running time.
In addition, these high heat losses are known to cause the buildup of carbon which can result in plugged turbine nozzles. This carbon build-up thereby can prevent reliable turbine operation. In order to avoid these heat losses, it is now known that a generally spherically-shaped combustor is an advantageous arrangement.
In this connection, a generally spherically-shaped combustor is well suited to minimize the mass of metal adjacent the flame to thereby minimize the detrimental thermal inertia effect. Furthermore, the surface/volume is minimized and hence steady state heat loss can also be minimized which further demonstrates the advantages of the spherical shape. As a further improvement, the use of a thin combustor wall liner has previously been disclosed in commonly owned, copending patent application U.S. Ser. Nos. 324,806 and 447,654, filed Mar. 17, 1989 and Dec. 8, 1989, now U.S. Pat. Nos. 4,955,202 and 5,024,058, issued Sep. 11, 1990, and Jun. 18, 1991, respectively.
In this earlier patent application, the thin combustor wall liner is provided immediately adjacent the combustion chamber inner wall. After ignition, the oxidant cooling path about the combustion chamber is thermally isolated from the thin combustor wall liner by a gap between the liner and the combustion chamber wall such that, during warmup, the liner is not cooled. Hence, since the combustor wall liner is thin and uncooled, the liner is able to heat up very quickly.
Being unstressed and formed of a suitable high temperature material, the liner can be operated at very high temperatures on the order of 1900.degree. F. Furthermore, as the liner is heated, it expands to close the gap between the liner and the combustion chamber wall to permit the liner to then be cooled by the oxidant cooling path about the combustion chamber. As a further advantage, the oxidant cooling path permits significant heat input into the oxidant prior to introduction into the combustion chamber once the liner is heated.
While this represents a most significant advancement in the field, it may not be desirable in every instance to utilize a liner in a stored energy combustor. It is nonetheless important that the hottest practical combustor wall temperature and the fastest possible warmup be achieved in order to minimize undesirable combustion inefficiencies, i.e., free carbon and oxygen, while permitting very fuel rich operation. Thus, where the thermal transient becomes critical, it is important to have some means of variable heat transfer to and from the combustor wall.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.